Method and apparatus for electrodischarge machining

ABSTRACT

An electric discharge machining apparatus having: a machining condition storage device ( 13 ) including a machining condition database in which machining condition data are stored; an input-output device ( 14 ) for reading either of shape data of a tool electrode ( 9 ) and machining shape data of a subject (W) for machining; a shape computing device ( 15 ) for extracting a plurality of sections from the shape data, mesh-dividing the sections into split elements, giving mesh data of solidness or hollowness and extracting machining shape characteristic from the mesh data; and a machining condition setting device ( 12 ) for selecting a machining condition while making the machining shape characteristic correspond to machining condition data in the machining condition database of the machining condition storage device ( 13 ). Even when the machining shape is complex, more efficient machining can be performed because an appropriate machining condition can be set.

TECHNICAL FIELD

The present invention relates to improvement in electric dischargemachining method and apparatus in which a machining condition can be setby use of graphic data of a tool electrode or a subject for machininggenerated by CAD or the like.

BACKGROUND ART

In electric discharge machining, a machining condition, an oscillatingcondition, etc. to be set are determined in accordance with the shape ofa tool electrode and electric discharge energy at the time of machining.For example, a high-energy machining condition is used in roughmachining and a low-energy machining condition is used in finalmachining for selecting an oscillating condition to make the shape of asubject for machining analogous to the shape of the tool electrode inaccordance with the target machining shape of the subject.

The machining condition used in rough machining is determined inaccordance with the expected shape of the subject, the depth ofmachining, the number of tool electrodes used in machining and thescaling-down margin as the downsizing quantity for the final shape andthe tool electrode. The machining condition used in final machining isdetermined in accordance with target accuracy in the final machiningshape of the subject, surface roughness and the degree of abrasion ofthe tool electrode. With respect to the oscillating condition, therelative movement between the tool electrode and the subject iscontrolled to obtain quadrilateral or polygonal oscillation whenangularity of the final machining shape of the subject is regarded asimportant, and the relative movement between the tool electrode and thesubject is controlled to obtain circular-arc, elliptic or sphericaloscillation when the final machining shape of the subject has roundness.

Further, in the case where the area of machining at an initial stage ofmachining is so small that abrasion of the tool electrode becomesintensive when machining is performed under a rough machining condition,control, so-called lead-in control is performed so that machining isstarted under a low-energy machining condition before the machiningcondition is gradually changed to an original rough machining condition.Further, adaptive control or the like for discharge interrupt time, jumpmotion, etc. is performed.

In this manner, lots of machining conditions must be set for electricdischarge machining. Moreover, these machining conditions stronglydepend on the shape of the tool electrode and the aimed machiningcontent. Hence, technical skill is required for setting the machiningconditions.

To solve this problem, Japanese Patent Laid-Open No. 218517/1990 hasdisclosed an electric discharge machining method and apparatus in whichan operating person inputs information concerning materials of a toolelectrode and a subject for machining to be used, maximum machining areaat the time of rough machining and surface roughness at final machiningso that optimal electrical conditions and optimal oscillation quantitiesat multistage oscillation machining are obtained by calculation based onthe input information.

On the other hand, Japanese Patent Laid-Open No. 178731/1991 hasdisclosed an electric discharge machining apparatus in which a toolelectrode shape sensor provided in a machining tank is used or toolelectrode shape information in an NC program is used so that machiningis performed while machining conditions optimal for the case where thestate is replaced by a state of actual electric discharge machining areautomatically selected.

In the electric discharge machining method and apparatus disclosed inJapanese Patent Laid-Open No. 218517/1990, there was a problem that itwas necessary to generate a function for recognizing the area ofmachining and a machining condition corresponding to the machining areawhen the shape of machining was complex because the electric dischargemachining apparatus could not recognize three-dimensional information ofthe tool electrode and the machining shape of the subject when themachining content was input.

On the other hand, in the electric discharge machining apparatusdisclosed in Japanese Patent Laid-Open No. 178731/1991, graphic data ofa tool electrode generated by CAD or the like is used for generatingmachining conditions. However, shape data original to the graphic datais not effectively used but only information of surface area per unitheight of a tool electrode having a three-dimensional shape generated byCAD/CAM is used. Further, no disclosure has been made on the method,etc., for performing controlling over machining done by a complex-shapetool electrode, and for generating machining conditions.

DISCLOSURE OF THE INVENTION

The present invention is designed to solve the aforementioned problemsand an object of the invention is to provide an electric dischargemachining method and apparatus in which efficient machining can beperformed even in the case where the shape of machining is complex.

The electric discharge machining method according to the invention is anelectric discharge machining method for performing machining under amachining condition selected while making either of shape information ofa tool electrode and shape information of a subject for machiningcorrespond to machining condition data in a machining conditiondatabase, having: a first step of reading either of shape data of thetool electrode and machining shape data of the subject; a second step ofextracting either of shape characteristic of the tool electrode andmachining shape characteristic of the subject from the shape data; and athird step of performing machining under a machining condition selectedwhile making either of the shape characteristic of the tool electrodeand the machining shape characteristic of the subject correspond tomachining condition data in the machining condition database.

Further, the electric discharge machining method according to theinvention is an electric discharge machining method for performingmachining under a machining condition selected while making either ofshape information of a tool electrode and shape information of a subjectfor machining correspond to machining condition data in a machiningcondition database, having: a first step of reading either of shape dataof the tool electrode and machining shape data of the subject; a secondstep of extracting a plurality of sections from the shape data; a thirdstep of mesh-dividing the sections and giving mesh data of solidness orhollowness; a fourth step of extracting either of shape characteristicof the tool electrode and machining shape characteristic of the subjectfrom the mesh data; and a fifth step of performing machining under amachining condition selected while making either of the shapecharacteristic of the tool electrode and the machining shapecharacteristic of the subject correspond to machining condition data inthe machining condition database.

Further, in the electric discharge machining method according to theinvention, the most frequent shape characteristic obtained in either ofshape characteristic information of the tool electrode and machiningshape characteristic information of the subject on the basis of the meshdata is recognized as either of shape characteristic of the toolelectrode and machining shape characteristic of the subject.

The electric discharge machining apparatus according to the invention isan electric discharge machining apparatus having machining conditionstorage means including a machining condition database in which aplurality of pieces of machining condition data are stored, wherein theelectric discharge machining apparatus further has: input means forreading either of shape data of a tool electrode and machining shapedata of a subject for machining; shape computing means for extracting aplurality of sections from the shape data, mesh-dividing the sectionsinto split elements, giving mesh data of solidness or hollowness to eachof the split elements and extracting either of shape characteristic ofthe tool electrode and machining shape characteristic of the subjectfrom the mesh data; and machining condition setting means for selectinga machining condition while making either of the shape characteristic ofthe tool electrode and the machining shape characteristic of the subjectcorrespond to machining condition data in the machining conditiondatabase of the machining condition storage means.

Further, in the electric discharge machining apparatus according to theinvention, the most frequent shape characteristic obtained in either ofshape characteristic information of the tool electrode and machiningshape characteristic information of the subject on the basis of the meshdata is recognized as either of shape characteristic of the toolelectrode and machining shape characteristic of the subject.

Because the invention is configured as described above, machining shapecharacteristic can be extracted so that an appropriate machiningcondition can be set by use of more detailed shape information. Hence,there is an effect that more efficient machining can be performed evenin the case where the machining shape is complex.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration view showing an electric discharge machiningapparatus according to an embodiment of the invention;

FIG. 2 is a flow chart showing a process for setting a machiningcondition by machining condition setting means;

FIGS. 3A and 3B are perspective views showing an example of the shape ofa tool electrode and the machining shape of a subject for machining;

FIG. 4 is a view for explaining extraction of cross sections of the toolelectrode;

FIGS. 5A to 5C are views for explaining mesh-division;

FIG. 6 is a view showing an example of mesh data of cross sectionsobtained by mesh-dividing the tool electrode shape; and

FIGS. 7A to 7D are explanatory views showing an example of extraction ofmachining shape characteristic from mesh data of respective splitelements in a cross sectional component and a longitudinal sectionalcomponent.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a configuration view showing an electric discharge machiningapparatus according to an embodiment of the invention. In the drawing,the reference numerals 1, 2 and 3 designate motors; 4, a main shaftdriven in a Z-axis direction by the motor 1; 5, a work table driven inan X-axis direction by the motor 2; 6, a work table driven in a Y-axisdirection by the motor 3; 7, a machining tank placed on the work tables5 and 6; 8, a machining liquid; 9, a tool electrode attached to the mainshaft 4; 10, a machining electric source unit; 11, a numericalcontroller; 12, machining condition setting means; 13, machiningcondition storage means; 14, input-output means; 15, shape computingmeans; 16, registration means; 17, storage means; and W, a subject formachining. The machining electric source unit 10 supplies machiningelectric power between electrodes, that is, between the tool electrode 9and the subject W so that the subject W is subjected to electricdischarge machining while the tool electrode 9 and the subject W aremoved relative to each other by the motors 1, 2 and 3 controlled to bedriven by the numerical controller 11.

A machining condition database is stored in the machining conditionstorage means 13 in advance. An operating person inputs at least one ofitems for designating machining such as material of subject formachining, tool electrode material, scaling-down margin, machiningaccuracy, machining time, etc. from the registration means 16.

The input-output means 14 can fetch an NC program or the like from anexternal computing unit or the like through a recording medium, acommunication cable, etc. The time required for machining, the machiningconditions computed by the machining condition storage means 13, and soon, can be stored in the storage means 17 and can be output to anexternal computing unit or the like through a recording medium, acommunication cable, etc.

The shape computing means 15 is means for fetching graphic data of thetool electrode 9 or the machining shape of the subject W input by theinput-output means 14 and generated by CAD or the like, and forextracting characteristic shape elements from the machining shape. IGESwhich is a standard data format of CAD data, or another format can beused as the graphic data.

FIG. 2 shows a process for setting machining conditions by the machiningcondition setting means 12. First, in the input-output means 14, shapedata of the tool electrode 9 or machining shape data of the subject W isselected and the graphic data is read (S1). For example, when the toolelectrode 9 is machined and molded into a convex shape, the subject W ismachined into a concave shape. That is, by electric discharge machiningwith a hole shape portion of the tool electrode 9, a pillar shape isformed in the subject W, so that shape information for the toolelectrode 9 is different from shape information for the machining shapeof the subject W. In few cases, shape data of the machining shape ispresent in electric discharge machining, unlike NC data, or the like,for rough machining in cutting by a machine tool. The tool electrode isdesigned on the basis of a product shape in consideration of the partingline, the draft angle and the downsizing quantity and is used as shapedata. Hence, in most cases, shape data of the tool electrode 9 ispresent. In most cases, the subject W and the tool electrode 9 can shareinformation of shape data when information of a Z axis is inverted. Thedownsizing quantity is small, for example, to be not larger than 1 mm.Hence, shape elements smaller than the scale-down quantity has hardlyinfluence on machining. Hence, there is no problem even in the casewhere shape data of the subject is generated on the basis of shape dataof the tool electrode.

FIG. 3A shows an example of the shape of the tool electrode 9. FIG. 3Bshows an example of the machining shape of the subject W. Descriptionwill be made below on the case where the graphic data read in S1 isgraphic data of the tool electrode 9. As shown in FIG. 4, in the toolelectrode 9, k+1 cross sections corresponding to Z0 through Zk areextracted at intervals of a predetermined parting width in a Z-axisdirection which is an advancing direction of machining (S2). Althoughthe cross sections can be preferably calculated at intervals of requireddimensional accuracy, the cross sections may be calculated at intervalsof the downsizing quantity of the tool electrode or at intervals ofabout 1 mm because calculation is delayed if the divisor is too large.

Then, the cross-sectional shape obtained in accordance with themachining direction in S2 is divided by small mesh. Although the meshdivision width can be preferably set to be equal to required dimensionalaccuracy, the cross-sectional shape may be divided by the downsizingquantity of the tool electrode or by about 1 mm because calculation isdelayed if the divisor is too large. For example, as shown in FIGS. 5Aand 5B, the cross-sectional shape is divided into i+1 parts in an X-axisdirection and into j+1 parts in a Y-axis direction. When the positioncoordinates of the graphic data are included in a mesh shape obtained bydivision, the position coordinates (XD, YD, ZD) of the graphic data arechanged to the position coordinates (XM, YM, ZM) of the mesh data asshown in FIG. 5C. To indicate solidness, for example, information of “1”is given. On the other hand, in the case of hollowness, the positioncoordinates of the graphic data are not included in the mesh shapeobtained by division. In this case, for example, information of “0” isgiven in order to indicate hollowness. In this manner, mesh data ofrespective split elements (Xn, Ym, Zl) (in which n, m and l are integerssatisfying 0≦n≦i, 0≦m≦j, 0≦l≦k, respectively) can be obtained (S3).

On the other hand, when the graphic data is of a surface model, meshdata (for example, “1” or “0”) can be given to each split element ifmodel data conversion which is a known technique concerning CAD/CAM ismade so that the graphic data can be used as data of a solid model. FIG.6 shows an example of mesh data of cross sections obtained bymesh-dividing the shape of the tool electrode 9 in FIG. 3A in thismanner.

Then, the characteristic of the machining shape is extracted by use ofthe mesh data of the respective split elements given in S3. As shown inthe example of FIGS. 7A to 7D, a cross-sectional component and alongitudinal sectional component can be obtained on the basis of themesh data of the respective split elements (Xn, Ym, Zl) (in which n, mand l are integers satisfying 0≦n≦i, 0≦m≦j, 0≦l≦k, respectively)extracted in S3.

A concave portion is the case where at least one mesh data “0” ispresent in the mesh shape of the cross-sectional component (X-Y plane)and where adjacent and continuous mesh data “0” are surrounded by meshdata “1”. A convex portion is the case where at least one mesh data “1”is present in the mesh shape of the cross-sectional component (X-Yplane) and where adjacent and continuous mesh data “1” are surrounded bymesh data “0”.

When a concave portion is detected, it can be found that a place wheremesh data of k+1 cross sections (X-Y plane) of from Z0 to Zk are all “0”expresses a “hole shape” (FIG. 7A) and that a place where mesh data ofat least one of k+1 cross sections (X-Y plane) of from Z0 to Zk is “1”expresses a “bag shape” (FIG. 7B).

After the shapes of concave portions are extracted throughout the wholeshape, the number of concave portions is counted. When at least oneconcave portion is present, information of “concave portion present” isadded to the shape information of the tool electrode. When a pluralityof concave portions are present, numbers are assigned to the shapes ofthe concave portions and information of the characteristic of shape suchas “bag shape”, “hole shape”, or the like, and information of the sizeof shape (such as the number of meshes) are given to the shape of eachof the concave portions. On this occasion, order of priority is given inaccordance with the size of the shape of each concave portion.

On the other hand, when a convex portion is detected, the characteristicof the tool electrode shape such as a rib shape shown in FIG. 7C or anarea-change shape shown in FIG. 7D can be extracted.

Convex portions are extracted throughout the whole shape and the numberof convex portions is counted in the same manner as in the case ofshapes of concave portions. When at least one convex portion is present,information of “convex portion present” is added to the shapeinformation of the tool electrode. When a plurality of convex portionsare present, numbers are assigned to the shapes of the convex portionsand information of the characteristic of shape such as “rib shape”,“area-change shape”, or the like, and information of the size of shape(such as the number of meshes) are given to the shape of each of theconvex portions. On this occasion, order of priority is given inaccordance with the size of the shape of each convex portion.

Generally, the tool electrode shape is constituted by various shapeelements as described above. When the aforementioned combination ofshape characteristics is complex, the most frequent shape characteristicobtained on the basis of shape characteristic information according tomesh data in consideration of the frequency (of the number correspondingto the shape characteristic allocated to the shape) and size (forexample, in accordance with frequency×size) is recognized as thecharacteristic of the tool electrode shape (S4).

The S2 to S4 can be performed by the shape computing means 15 includedin the machining condition setting means 12.

Machining conditions corresponding to the characteristic shape element,machining area, machining depth, etc., of the tool electrode (that is,machining shape) extracted in S4 are called from the machining conditiondatabase in the machining condition storage means 13 and set (S5).Machining conditions corresponding to characteristic shape elements canbe experimentally determined and stored in the database of the machiningcondition storage means 13 in advance.

In this manner, when a characteristic machining shape is extracted and amachining condition adapted to the characteristic machining shape isselected, more efficient machining can be made because an appropriatemachining condition can be set even in the case for a complex machiningshape.

Industrial Applicability

As described above, the electric discharge machining method andapparatus according to the invention is adapted for use in electricdischarge machining work.

What is claimed is:
 1. An electric discharge machining method for performing machining under a machining condition selected while making either of shape information of a tool electrode and shape information of a subject for machining correspond to machining condition data in a machining condition database, characterized by comprising: a first step of reading either of shape data of said tool electrode and machining shape data of said subject; a second step of extracting either of shape characteristic of said tool electrode and machining shape characteristic of said subject from said shape data; and a third step of performing machining under a machining condition selected while making either of said shape characteristic of said tool electrode and said machining shape characteristic of said subject correspond to machining condition data in said machining condition database.
 2. An electric discharge machining method for performing machining under a machining condition selected while making either of shape information of a tool electrode and shape information of a subject for machining correspond to machining condition data in a machining condition database, characterized by comprising: a first step of reading either of shape data of said tool electrode and machining shape data of said subject; a second step of extracting a plurality of sections from said shape data; a third step of mesh-dividing said sections and giving mesh data of solidness or hollowness; a fourth step of extracting either of shape characteristic of said tool electrode and machining shape characteristic of said subject from said mesh data; and a fifth step of performing machining under a machining condition selected while making either of said shape characteristic of said tool electrode and said machining shape characteristic of said subject correspond to machining condition data in said machining condition database.
 3. An electric discharge machining method according to claim 2, characterized in that most frequent shape characteristic obtained in either of shape characteristic information of said tool electrode and machining shape characteristic information of said subject on the basis of said mesh data is recognized as either of shape characteristic of said tool electrode and machining shape characteristic of said subject.
 4. An electric discharge machining apparatus comprising machining condition storage means including a machining condition database in which a plurality of pieces of machining condition data are stored, characterized in that said electric discharge machining apparatus further comprises: input means for reading either of shape data of a tool electrode and machining shape data of a subject for machining; shape computing means for extracting a plurality of sections from said shape data, mesh-dividing said sections into split elements, giving mesh data of solidness or hollowness to each of said split elements and extracting either of shape characteristic of said tool electrode and machining shape characteristic of said subject from said mesh data; and machining condition setting means for selecting a machining condition while making either of said shape characteristic of said tool electrode and said machining shape characteristic of said subject correspond to machining condition data in said machining condition database of said machining condition storage means.
 5. An electric discharge machining apparatus according to claim 4, characterized in that most frequent shape characteristic obtained in either of shape characteristic information of said tool electrode and machining shape characteristic information of said subject on the basis of said mesh data is recognized as either of shape characteristic of said tool electrode and machining shape characteristic of said subject. 